This invention relates to an exposure apparatus for use in the manufacture of semiconductor devices and, more particularly, to a projection exposure apparatus and method for transferring, by projection, a photomask pattern onto a wafer. Also, the invention relates to a semiconductor device manufacturing method. More specifically, the present invention is concerned with a scan type exposure apparatus and method, or to a semiconductor device manufacturing method using the same, wherein, for projection exposure of a wafer to a photomask pattern, the mask and a wafer are scanningly moved in synchronism relative to a projection optical system (projection exposure system). As an example, the invention is suitably applicable to a scan type projection exposure apparatus which is usable in a lithographic process, among device manufacturing processes for the manufacture of semiconductor devices such as ICs or LSIs, image pickup devices such as CCDs, display devices such as liquid crystal panels, or magnetic heads, for example, to perform wafer alignment when a pattern of a reticle (first object) is to be projected by a projection optical system onto the surface of a wafer (second object).
The density of integration of a semiconductor device such as an IC or an LSI has increased considerably. As regards projection exposure apparatuses, filling the major role in the fine processing technology for semiconductor wafers, there are various exposure apparatuses developed, such as a unit-magnification projection exposure apparatus (mirror projection aligner) wherein an exposure process is performed while scanningly moving a mask and a photosensitive substrate relative to a unit-magnification mirror optical system having an arcuate exposure region, or a reduction projection exposure apparatus (stepper) wherein an image of a mask pattern is formed through a refraction optical system on a photosensitive substrate and the photosensitive substrate is exposed in a step-and-repeat process.
The size of the chip pattern of one semiconductor device is increasing. Thus, for a projection exposure apparatus, it is required to enlarge the exposure area by which a large area pattern of a mask can be printed on a photosensitive substrate.
In order to meet these requirements, various proposals have been made in relation to a step-and-scan type scanning projection exposure apparatus (exposure apparatus) which provides a high resolution and an enlarged picture field size. In such a scan type exposure apparatus, a pattern on the surface of a reticle is illuminated with a slit-like light beam and, while the pattern as illuminated with the slit-like light beam is projected by a projection system (projection optical system), it is transferred onto a wafer through a scanning operation.
Many proposals have been made on such a scan type projection exposure apparatus, and there is an example in which a unit-magnification scan type exposure apparatus with a conventional reflection projection optical system is modified and refraction elements are incorporated into the projection optical system, such that reflection elements and refraction elements are used in combination. Another example is a scan type exposure apparatus wherein a reduction projection optical system comprising refraction elements only is used and wherein both of a mask stage and a stage (wafer stage) for a photosensitive substrate are scanningly moved in synchronism with each other at a speed ratio corresponding to the reduction magnification.
FIG. 23 is a schematic view of a main portion of a scanning exposure apparatus. In the drawing, a mask (reticle) 1 on which an original is formed is supported by a mask stage 3. Wafer (photosensitive substrate) 13 is supported by a wafer stage 5. The mask 1 and the wafer 13 are disposed in an optically conjugate relationship with each other, with respect to a projection optical system 2. Slit-like exposure light 12 coming from an illumination system (not shown) and being elongated in the Y direction in the drawing, illuminates the mask 1 by which it is imaged upon the wafer 13 with a size corresponding to the projection magnification of the projection optical system 2. A scan exposure process is performed by moving both of the mask stage 3 and the wafer stage 5 relative to the slit-like exposure light 12, in other words, relative to the projection optical system 2, at a speed ratio corresponding to the optical magnification, to scan the mask 1 and the wafer 13. By this, the whole device pattern of the mask 1 is transferred onto a transfer region 10 on the wafer 13.
Practically, the scan exposure process is performed to two types of wafers as roughly classified:
(a1) Wafer to which no mask pattern has been transferred (hereinafter xe2x80x9cfirst waferxe2x80x9d); and
(a2) Wafer on which a mask pattern or patterns are already formed (hereinafter xe2x80x9csecond waferxe2x80x9d).
When a mask pattern is to be superposedly printed on a second wafer, patterns of a mask 1 and of a wafer 13 may be detected by using mark detecting means 15 and through an alignment optical system 4. The result of the detection may be processed by an operation processing circuit 16. On the basis of this and of the positions of the mask stage and wafer stage as monitored by laser interferometers 7 and 8, mask and wafer alignment may be done. Thereafter, the mask stage 3 and the wafer stage 4 may be moved in synchronism with each other under control by drive control means 17, to perform the scan exposure.
If a reduction projection optical system is used, it is necessary that a mask 1 to be used is larger than a pattern region, to be defined on a wafer 13, by an amount corresponding to the projection magnification. In order to support such a large mask 1, the mask stage 3 has to be large. Taking into account a drive system for such a mask, an increase in weight is large. This may result in a problem that sliding motion of the mask stage 3 during an actual exposure process causes a shift of the gravity center of the mask stage 3, which in turn may cause an error in attitude of the projection optical system 2, or a considerable shift of it.
Further, driving such a heavy mask stage 3 may cause a problem of vibration of the projection optical system 2, due to a reaction in accelerating the mask stage 3 to a certain speed, or pitching of the mask stage 3 itself. Also, such vibration may cause a change in attitude of the projection optical system 2, which in turn may cause a problem that an image is printed with deviation from a desired exposure region. An image shift on an exposure plane may also result from pitching of the mask stage. Such a deviation attributable to vibration, if it occurs in the scan direction, leads to deterioration of superposition precision. Vibration in a direction perpendicular to the scan direction causes a focus error (defocus and tilt) on the wafer surface. It results in degradation of exposure precision during first wafer processing and second wafer processing.
In order to avoid the effect of vibration of the projection optical system 2, attributable to driving the mask stage 3, it may be necessary that, from a start of acceleration, the mask stage 3 is moved to a position where the effect of vibration can be disregarded, and that the exposure process is initiated from that position. If driving the mask stage causes a large vibration of the projection optical system, a substantial time has to be set from a start of scan motion to a start of exposure. Thus, throughput will be lowered.
Also, the scan distance of the mask stage to the above-described position becomes longer. Since in a scan type exposure apparatus, the scan direction of a mask stage is usually reversed between an odd-number shot and an even-number shot, on a wafer, for enhancement of throughput, the prolongation of scan distance appears both on the opposite sides of the scan direction. This leads to bulkiness of the whole exposure apparatus.
It is an object of the present invention to solve at least one of the above-described problems, and to avoid the effect of vibration, attributable to stage driving, without a decrease of throughput or without an increase of scan distance.
It is another object of the present invention to provide a scan type projection exposure apparatus or a device manufacturing method using the same, by which a high precision exposure process or manufacture of high precision semiconductor devices is assured.
In accordance with an aspect of the present invention, there is provided a scan type exposure apparatus, comprising: a first movable stage on which a first object is to be placed; a second movable stage on which a second object is to be placed; a projection optical system for projecting a pattern of the first object onto the second object; a scanning mechanism for scanningly moving said first and second movable stages in a timed relation with each other, relative to said projection optical system, while the pattern of the first object is projected by said projection optical system onto the second object; storing means for storing therein data corresponding to a change in exposure condition as measured beforehand and to be produced by moving at least one of said first and second movable stages; and control means for controlling drive of said first and second movable stages in an actual exposure process, while reflecting a correction value, as determined on the basis of the data stored, to the drive of at least one of said first and second movable stages.
A scanning exposure method or a semiconductor device manufacturing method having similar features as described above may be provided within the scope of the present invention.
In one preferred form of this aspect of the present invention, the correction value is determined with respect to plural accelerations or speeds of at least one of said first and second movable stages, and the correction value is set variably in accordance with the accelerations or speeds and with directions of them.
In another preferred form of this aspect of the present invention, the correction value is determined with respect to a deviation of a projected image of the pattern of the first object, upon the second object.
In a further preferred form of this aspect of the present invention, the correction value is determined with respect to a focus error of a projected image of the pattern of the first object, upon the second object.
In a yet further preferred form of this aspect of the present invention, the scan exposure is performed while controlling a quantity of exposure light in accordance with a speed of at least one of said first and second movable stages.
In accordance with another aspect of the present invention, there is provided a scan type projection exposure apparatus, comprising: a first movable stage on which a first object is to be placed; a second movable stage on which a second object is to be placed; a projection optical system; scanning means cooperable with said projection optical system, for scanningly moving said first and second movable stages in a timed relation with each other and at a speed ratio corresponding to a projection magnification of said projection optical system so that a pattern of the first object is projected by said projection optical system onto the second object; detecting means for measuring a position of an image plane of the first object defined by said projection optical system; storing means for storing therein image plane positions as measured by said detecting means while scanningly moving said first movable stage, as correction values related to image plane positions at different scan positions of said first movable stage; and driving means for moving the second object in a direction of focus on the basis of the image plane positions stored in said storing means, to set the second object with respect to the image plane position.
In one preferred form of this aspect of the present invention, before image plane position measurement during scanning motion of said first movable stage, said detecting means detects image plane position information of the first object defined by said projection optical system as said first movable stage is held fixed, on the basis of which image plane position information said detecting means calculates information related to image plane positions with respect to different scan positions of said first movable stage.
In another preferred form of this aspect of the present invention, said detecting means includes an illumination light source for projecting illumination light onto the first object, a first slit for passing a portion of the illumination light and provided to the surface of the first object, and light receiving means for detecting light, of the illumination light, passed through said first slit and through said projection optical system, wherein said detecting means detects information related to image plane positions of the first object with respect to different scan positions of said first movable stage, as defined by said projection optical system, on the basis of a signal produced by said light receiving means.
In a further preferred form of this aspect of the present invention, said detecting means includes an illumination light source for illuminating a second slit mark provided on said second movable stage, and light receiving means for detecting light coming from said second slit mark and through said projection optical system, wherein said detecting means detects information related to image plane positions of the first object with respect to different scan positions of said first movable stage, as defined by said projection optical system, on the basis of a signal produced by said light receiving means.
In a further preferred form of this aspect of the present invention, said light receiving means detects light passed through said first slit and through said projection optical system and then reflected by a reflection surface, provided on said second movable stage and having a surface step structure, and then again passed through said projection optical system and through said first slit.
In a further preferred form of this aspect of the present invention, the first object is formed with a first pattern for image plane position measurement and an observation window for observation of a surface of said second movable stage, wherein said second movable stage is formed with a second pattern for image plane position measurement, wherein said detecting means includes an observation system for simultaneous observation of said first and second patterns, such that said detecting means detects information related to image plane positions of the first object with respect to different scan positions of said first movable stage, as defined by said projection optical system, on the basis of said first and second patterns observed by said observation system.
In accordance with a further aspect of the present invention, there is provided a device manufacturing method, including aligning a reticle and a wafer and then projecting and printing a pattern of the reticle onto the wafer by using a scan type projection exposure apparatus as described above, and then developing the exposed wafer.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.